The Merits of a Basic Fitting Pattern
The chief use of the sloper is in flat-pattern design, where the idea is that every pattern properly made from it will fit the figure the sloper fits. But having such an accurate, tangible record of your own shape can be a powerful fitting tool for existing patterns, as well. After all, if you have a sloper that fits, you've already solved your most important and most complex fitting problems. Why should you have to re-solve these problems each time you alter a pattern?
Your sloper is a two-dimensional dress form
I think of a sloper as a flat dress form, cut into front and back pieces. Lay your pattern on your "flat form," and you can see immediately whether the pattern will fit you because you can see how and where it fits the sloper, and where it doesn't. You'll almost certainly have to redistribute the sloper's dart shaping to line up with the pattern's (see What you need to know about pivoting darts below), but once that's done, it's easy to see the variance between the two shapes, even if you don't yet know how to fix it.
|What you need to know about pivoting darts
Darts reduce width and length wherever you don't need it (at the sides of the bust or at the waist, for example), after you've provided the extra length required to fit across a "bump" such as bust, tummy, rear, hip, or shoulder blade. The accumulated size (measured by the angle of each dart opening) of all the darts pointing to a single bump represents the total extra width and length that bump requires for coverage. This amount is called "dart control," and in many slopers it's gathered into one big dart for each bump, as shown in drawing at far left below.
Fortunately, you can divide that one dart into two or more smaller darts without changing the total dart control, as long as their combined angles equal the total dart-control angle. Further, the position of the darts doesn't matter. Provided they all point toward the apex of the bump, the dart legs can be pivoted to end in any surrounding seam, as in the examples of altered slopers above, all of which have the same amount of dart control. In patterns, all or part of the total dart control can also be taken up in gathers, pleats, or ease at any surrounding seam, or left unstitched. The unstitched portions can also be pivoted around the bump, resulting in longer seams (and loose wrinkles) at shoulder, armscye, side, or waist, wherever the designer positions it.
Finally, dart control in a sloper extends to the apex of the bump it fits (for example, a bodice sloper's bust point), which makes pivoting easy. When converted to garment darts, the dart's point is shifted from the apex by at least 1/2 in. to smooth the fabric at the apex.
|To pivot darts, trace the sloper onto tissue paper, then adjust the tissue copy. Slash from the seam edge where you want to position the new dart to the dart apex, leaving a small paper hinge at the apex. Pivot the existing dart closed until the new dart opens up sufficiently. Notice how pivoting changes the angle of the sloper side seam, relative to the center front.|
|Comparing sloper and pattern
When you lay your sloper over any commercial pattern, it's difficult to see the relationship between them until the dart control on the sloper has been divided and pivoted to match the way it was positioned on the garment by the designer. After aligning the front and back centers on your pattern and sloper, the next step is to pivot the control so the side seams are parallel (but not necessarily aligned). But where to put the new dart(s)?
Obviously, if the pattern has any visible darts or gathers, slash your sloper tracing parallel to them but pointing to its apex, then distribute as much control to that section of the sloper as you need to align the side seams. If you can't see the dart control, it's been left unstitched, so look for lengthened shoulders and armscyes, unshaped waists and/or side seams, and (on jackets) eased roll lines, all common places for unstitched dart control. These features are also clues that some control has been positioned here, even if there's a visible dart elsewhere in the pattern.
In either case, slash and pivot your sloper tracing (as described in the drawings above) in the unstitched, dart-controlled areas just described, as you would for visible darts, until the side seams are parallel. Even if your dart-control total is different from the pattern's, as long as you've distributed yours in approximately the same directions away from the apex, you're ready to match slopers when the sides are parallel, as in Step 2 and Step 3.